Countdown for Rocket Planes

Xcor Aerospace’s EZ-Rocket is like those early PCs-simple, basic, and from the standpoint of the conventional aerospace business, practically microscopic. Its twin rocket engines, fueled by alcohol and liquid oxygen, separately produce only one-thousandth the thrust of each of the space shuttle’s three main engines. But unlike their shuttle counterparts, the EZ-Rocket engines can be fully controlled and even shut down and restarted in flight. Still, the EZ-Rocket is just a demonstration vehicle. The tiny craft is designed to rack up experience for building a two-seat suborbital space plane called Xerus, which is now in development.

For the Xerus, Xcor Aerospace is developing a rocket engine with five times the power of EZ-Rocket-an engine that can be throttled up and down through a wide range of speeds. A cluster of four or five such engines would lift the rocket plane to an altitude of 100 kilometers; then smaller rockets would allow the craft to maintain stability during an edge-of-space jaunt.

Xcor Aerospace is pursuing the two-person Xerus even though it will not meet the three-person criterion of the X-Prize. Prize or no prize, Greason, Rutan, and their handful of coworkers see plenty of financial incentive. Greason says the Xerus could launch a small satellite payload-about 10 kilograms-into a low orbit using a booster rocket on the satellite. Similarly small satellites are used for university research projects, which often must wait years to piggyback onto a larger satellite launch. And the Xerus itself could also be used for research such as collecting atmospheric data or carrying out engineering experiments that require brief periods of time in a zero-gravity environment.

The real target, though, is tourism. Greason says the Xerus could provide tourists with half-hour joyrides-three minutes of weightlessness and a chance to see the Earth’s curvature and the darkness of space-then land on an ordinary runway. One Xerus alone, he says, could earn $24 million a year in tourist revenues on development costs of less than $10 million. Fueled by such visions, Xcor Aerospace hopes within three years to have flown and tested Xerus and readied the craft for production. “We decided to do the smallest steps we could, with as many of them as possible generating revenues,” Greason explains. If Xerus works and tourist profits roll in, he says, the company’s developers would begin to tackle the ultimate task-getting into orbit.

The idea of “smallest steps,” of course, has a certain historical resonance when it comes to space technology. But while Xcor Aerospace focuses on the incremental approach, several competing companies are already pursuing the grand vision: a craft that can go all the way into orbit. One player is Pioneer Rocketplane in Solvang, CA. The company has designed a tourist or cargo-carrying rocket-and-jet hybrid called Pathfinder, which will take off with traditional jet engines. Once at a cruising altitude of about 5,500 meters, a fuel tanker plane will rendezvous with the Pathfinder and pump liquid oxygen into an empty tank on board the craft. Then, propelled by a combination of liquid oxygen and kerosene, the Pathfinder will light its rocket motor and soar to an altitude of 139 kilometers, where it could also release an unmanned upper stage to deliver a 2,280 kilogram payload into orbit.

Like Xcor Aerospace, Pioneer is starting with a smaller version-the Rocketplane XP-which will compete for the X-Prize. Though neither the XP nor the Pathfinder has reached even the prototype stage, Pioneer Rocketplane is considered a serious player. Its CEO, Mitchell Burnside Clapp, was responsible for an Air Force design of an airplanelike reusable rocket that later evolved into the Pathfinder concept. Because of that design, Pioneer Rocketplane is a leading competitor for a Defense Advanced Research Projects Agency project to develop an inexpensive rocket-propelled satellite launcher. (The agency was expected to announce the award of two final design contracts on March 1.)

Most of the reusable-rocket players are thinking in terms of carrying people-both pilots and tourists. But Germany’s Astrium is expressly leaving out human cargo. Instead, it is developing an autonomous rocket craft called Hopper, designed to provide cheap satellite launches. The first step in this direction is the Phoenix, a one-sixth-scale version of the Hopper. The Phoenix is mainly a test bed for autonomous landing technology. The craft’s designers are incorporating laser-based altimeters-altitude sensors-and digital Global Positioning System equipment together with intelligent-navigation algorithms that enable the craft to make a gliding runway landing without help from humans or equipment on the ground. The first test of the vehicle, which is under construction, is expected next year: a helicopter will drop the Phoenix from an altitude of about 1,400 meters, leaving it to land on its own. Astrium estimates that the full-size Hopper could launch satellites in 15 to 20 years, at half today’s launch costs.

And NASA isn’t sitting on the sidelines. Although the exact shape of a successor program to the ill-fated X-33 is still being worked out by agency administrator Sean O’Keefe, who took the helm in late 2001, NASA had begun to fashion long-term plans for a bigger, more ambitious craft even before the Columbia disaster. The Orbital Space Plane is just a blank sheet of paper now, but the idea is that it would be ready to deliver crew and small amounts of cargo to the International Space Station by 2012.

If it does fly by 2012 or sooner, the Orbital Space Plane would get to orbit atop a conventional expendable rocket. But NASA hopes eventually to replace that rocket with a reusable system. To do this, researchers at NASA’s Marshall Space Flight Center in Huntsville, AL, are simplifying and streamlining rocket engine design and incorporating built-in diagnostic systems to detect problems such as cracks, leaks, and stuck valves. Such systems would yield tremendous savings compared to the space shuttles, whose engines are dismantled and inspected after every mission by hundreds of engineers. “The goal is to bring rocket engine reliability into the same category as today’s jet engines,” says Garry Lyles, who is in charge of propulsion systems for NASA’s program to develop technology for future launch vehicles. Right now anyway, NASA’s plans call for a reusable space-shuttle replacement by 2025.